The correct answer to this open question is the following.
Okonkwo says: "They are fools...They had been warned that danger was ahead. They should have armed themselves with their guns and their machetes even when they went to market."
What this quote shows about Okonkwo is the following.
1.-
Although Okonkwo tried to warn people about the danger coming, they never paid heed to his warnings, and fatality ended up coming to them.
2.-
If people would have paid attention to the urgency of Okonkwo's warmings, they could have been prepared to defend themselves and the result probably would be different.
As we know in grammar, a dependent clause has to have a subject, verb, and complement because it can't stand alone.